Key-operable security switches are known which incorporate locks of the kind having a barrel which is rotatably mounted in a housing, the barrel and housing being interconnected, when in a relatively locked position, by a plurality of tumblers which extend through apertures formed in the wall of the barrel and which prevent relative rotation between the barrel and the housing until a key is inserted into a slot or aperture formed in the barrel and successively engage said tumblers and move them into positions in which they do not interconnect the barrel and the housing. In such an arrangement, once the barrel is free to rotate it can also be arranged to move axially relative to the housing and the rotary and/or axial movement can be utilised to make or break electrical circuits which can be used to perform the required function or functions of the associated switch. Such a mechanism however suffers from the disadvantage that one edge of the key slides across the aforesaid tumblers as it is engaged with or disengaged from the barrel of the lock, thereby in time tending to cause wear on the tumblers (which means that they normally have to be formed in metal) and/or on the key which may eventually result in malfunctioning of the mechanism. Furthermore the provision of tumblers in a rotatable barrel in a housing leads, to some extent, to a relatively bulky mechanism which may not necessarily fit easily and unobtrusively into apparatus which the security switch is intended to control.
The object of the present invention is to provide a security switch in an improved form which avoids the aforementioned disadvantages.